1. Field of the Invention
The invention relates to an injection system for an internal combustion engine, having one fuel pump per engine cylinder to be supplied, which pump is controlled electronically; having an injection nozzle, which is provided with a nozzle needle; and having a connecting line between the fuel pump and the injection nozzle.
2. Description of the Prior Art
Such an injection system is an individual-cylinder system, in which the injection pump is driven by a camshaft, for instance. Upon actuation by a cam, the fuel to be injected is put under pressure in the fuel pump and delivered to the injection nozzle. The onset and end of pumping by the fuel pump can be controlled for instance by means of a slide valve, which in a first state connects the pumping chamber of the pump with a return line, so that fuel pumping does not occur, and in a second state closes the connection to the return line, so that a pressure buildup is possible. In this way, the injection onset and also, via a control of the length of the injection event, the injection quantity as well can be controlled. However, the injection pressure is a function of the rpm of the camshaft that drives the pump. The course of injection and a pre-injection can also be varied only in the pump. This leads to restrictions in terms of the pre-injection quantity and the shaping of the course of injection, as well as unacceptable deviations between the various individual cylinders of the engine.
The object of the invention is thus to refine a known injection system in such a way that not only the injection quantity and the injection onset but also the injection pressure, course of injection, pre-injection, post-injection and multiple injection can be varied in the desired way.
The injection system of the invention has the advantage that by suitable actuation of the electronically controlled valve at the injection nozzle, the fuel volume furnished by the fuel pump can be injected as desired; additional parameters for controlling the course of injection are furnished, which are independent of the onset and end of pumping by the fuel pump. Unlike conventional systems, in which the nozzle needle has opened automatically as soon as a predetermined pressure is exceeded after the onset of pumping by the fuel pump, and the nozzle needle also closes automatically again as soon as a certain minimum pressure toward the end of pumping is undershot, with the injection system of the invention it is now possible to inject essentially independently of the pumping rate of the fuel pump. It is also possible, for the same fuel pump dimensions, to utilize the entire stroke of the pump and thus enhance the performance of the system for the same dimensions. Another advantage is that only slight modifications compared with the conventional systems are necessary. The previously used injection nozzle must merely be replaced by an electronically regulated injection nozzle.
In comparison with so-called common rail systems, in which a single fuel pump is used to supply a high-pressure collection chamber, from which the fuel is then injected into the individual cylinders, the system of the invention offers greater operating safety, since in the event of later failure of the fuel pump, because of the modular design of the system only the corresponding cylinder of the engine is affected. The course of injection can be controlled variably in the same way as is possible in a common rail system.